Display contrast

ABSTRACT

Display devices with improved display contrast and methods of manufacturing the display devices. Some embodiments include a method of manufacturing a light emitting diode (LED) array. The method includes forming a first mesa area of a first LED and a second mesa area of a second LED, where a trench is defined between the first and second mesa areas. At least a portion of the trench is filled with a non-transparent or substantially non-transparent polymeric material that absorbs light emitted from the first and second LEDs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 15/376,501, filed Dec. 12, 2016, which is a continuation of U.S. application Ser. No. 13/261,922, filed Jun. 20, 2014, which is a National Phase application of International Application No. PCT/GB2012/053192, filed Dec. 19, 2012, which claims the benefit of United Kingdom Application No. 1121864.1, filed Dec. 20, 2011, each incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to electronic components with improved display contrast and a method of manufacturing such electronic components. More particularly, the present invention relates to electronic components having improved display contrast by using a non-transparent or substantially non-transparent material to block light from an emitter source to surrounding components such as emitters, sensors or components of this nature.

BACKGROUND OF THE INVENTION

Polyimide is commonly used for planarizing semiconductor devices and to provide electrical isolation between interconnected structures. A good example has been demonstrated by Horng et al. in US patent application 2011/0092005, which is incorporated herein by reference. A parallel addressed array of macro LEDs with improved reliability was achieved by using polyimide to fill the gap between the macro LEDs. Another common application is polyimide encapsulation of LEDs to improve the light extraction efficiency because of the increased refractive index such as described by Chen et al. in US patent application 2011/0024720, which is incorporated herein by reference. In contrast to the proposed present invention the polyimide used in these applications is transparent or what is known as having a high optical clarity.

This document is applicable to all LED arrays. For the description provided it is mainly concerned with the difficulties in manufacturing micro-LED structures which in this case will refer to any LED structure of less than 100 microns diameter. There are a number of known and existing problems with micro-LED arrays. For example, there is strong optical crosstalk between adjacent pixels in conventional LED arrays, resulting in the LED display having poor contrast. To form a matrix-addressable LED array, isolated LED mesa columns need to be formed by dry etch. The large height difference, the sloped mesa and the sharp edges formed in the trench cause undesirable light scattering (bars surrounding the pixels), and thus reduce the display contrast of the LED array.

A further known problem with LED arrays is a reliability issue associated with the isolation layer. Conventionally, the isolation layer of p-contacts from n-contacts of a matrix LED array is made from dielectric materials (e.g. silicon oxide or silicon nitride). For instance, Dawson et al. in US patent US2006/0110839 A1, which is incorporated herein by reference, uses SiO₂ to isolate the mesa with sloped sidewall. Although the sloped mesa can alleviate the step coverage issue of the dielectric layer normally associated with standard techniques, the device made this y can still have reliability issues, resulting in undesirable electric crosstalk or shorting. This is mainly due to the fact that the thin dielectric layer cannot reliably cover the mesa with a large height, and it may be stripped off during subsequent process due to possible adhesion issues. All of these factors mean that the devices need to be carefully manufactured to ensure that the sidewall is suitably angled and that there are no contaminants (e.g. pin-holes) which could cause electrical crosstalk.

The present invention seeks to overcome these said disadvantages and problems.

It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems. It is a further object of at least one aspect of the present invention to provide improved micro-LED arrays with improved display contrast and reduced optical cross-talk.

It is a further object of at least one aspect of the present invention to provide an improved method for manufacturing micro-LED arrays with improved display contrast and reduced optical cross-talk.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an array of integrated LED devices. This may involve a micro-LED array comprising:

at least two raised mesa areas;

located between the at least two raised mesa areas there is a trench;

on the upper surface of the at least two raised mesa areas there are pixels and N-bus formations along with an annealed metal area and a p-metal layer;

wherein the trench is at least partially filled with a non-transparent or substantially non-transparent material capable of blocking light emitted from within the micro-LED array.

The present invention therefore resides in the provision of using a non-transparent or substantially non-transparent material to block light from an emitter source to surrounding components such as emitters, sensors or components of this nature. This non-transparent or substantially non-transparent material is used to reduce unwanted crosstalk and thereby provide improved display contrast for micro-LED arrays and the like.

The non-transparent or substantially non-transparent material may therefore fill the trench in adjacent pixels. Although the actual thickness of the deposited non-transparent or substantially non-transparent material is not important sufficient material should be introduced so that redirected light should be absorbed and prevented from being emitted from the upper surface.

The non-transparent or substantially non-transparent material may fully occupy the trench or may simply form a layer.

The non-transparent or substantially non-transparent material may be seen as functioning as an interlayer dielectric.

The non-transparent or substantially non-transparent material may be selected from any appropriate material that is capable of blocking light. For example, the material may be selected from any suitable polymeric material such as anyone of or combination of the following: polyimide; epoxy; and benzocyclobutene.

In particular embodiments there is a combination of different polymers forming a light blocking layer. For example, there may be a combination of polymer and other dielectric layers such as but not limited to silicon nitride and/or silicon dioxide.

The non-transparent or substantially non-transparent material forms a layer which is non-transparent or substantially non-transparent to light at the emission wavelength of the micro-LED array. The non-transparent or substantially non-transparent material may therefore be matched to block the light emitted from the micro-LED array. The material may be designed to have a non-transparent surface layer or graded non-transparent layer.

A further advantage of the non-transparent or substantially non-transparent material in polymeric form is that the polymeric layer allows metals such as deposited p-metal layer to be conformably deposited thereby further reducing the light scattering from the trench (i.e. cavity). The polymeric material may also provide optical and electrical isolation between emitters of varying wavelength emissions and/or of different structural design and/or other integrated components.

It has been found that the deposited non-transparent or substantially non-transparent material may also function to effectively isolate each pixel and p-contact from n-contacts, thereby eliminating the undesirable electric crosstalk and improving the device reliability.

According to a second aspect of the present invention there is provided a method of manufacturing a micro-LED array comprising:

forming at least two raised mesa areas wherein located between the at least two raised mesa areas there is a trench;

on the upper surface of the at least two raised mesa areas forming pixels and N-bus formations along with an annealed metal area and a p-metal layer; and

wherein the trench is at least partially filled with a non-transparent or substantially non-transparent material capable of blocking light emitted from within the micro-LED array.

The manufactured micro-LED array may be as defined in the first aspect.

The mesa areas may be formed using a dry etch technique.

The non-transparent or substantially non-transparent material may be deposited into the trench using any suitable deposition technique to form a layer or fully fill the trench up to the same level as the height of the mesa areas.

The non-transparent or substantially non-transparent material may be cured.

The pixels and N-bus formations may be formed on the upper surface of the mesa areas using any suitable technique.

A metal layer (e.g. a p layer) may be formed onto etched areas on the upper surface of the mesa areas.

According to a third aspect of the present invention there is provided a flip-chip device comprising non-transparent or substantially non-transparent material capable of blocking light.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIGS. 1 and 2 are micro-LED arrays according to the prior art showing significant crosstalk;

FIG. 3 is a micro-display image from a conventional matrix device using SiO₂ as the isolation layer between mesa and from the image where electric crosstalk and open circuit (due to metal coverage issue on the SiO₂) are evident;

FIG. 4 is a micro-display image from a micro-LED array device according to the present invention where there is no electric crosstalk and open circuit are observed;

FIG. 5 is a cross-sectional side view of a micro-LED array according to the present invention;

FIG. 6 is a top view of a micro-LED array according to the present invention; and

FIGS. 7 to 14 show a method of forming micro-LED arrays according to the present invention.

BRIEF DESCRIPTION

Generally speaking, the present invention resides in the provision of using a non-transparent or substantially non-transparent material to block light from an emitter source to surrounding components such as emitters, sensors or components of this nature. This non-transparent material is used to reduce unwanted crosstalk and thereby provide improved display contrast for micro-LED arrays and the like.

FIGS. 1 and 2 are views of arrays according to the prior art generally designated 100, 200 where there are a plurality of LEDs 112, 212 showing significant crosstalk between them. The LEDs 112, 212 when activated have a ‘halo’ effect and show poor display contrast. In the array 100 there is a block of LEDs 112 where there is poor contrast with as much as 20% of the light measured from the surrounding area outside the area of the LED 112.

FIG. 3 is a micro-display image 300 from a conventional matrix device according to the prior art using SiO₂ as the isolation layer between mesa and from the image. Electric crosstalk and an open circuit (due to metal coverage issue on the SiO₂) are evident due to the very poor image contrast.

FIG. 4 is a micro-display image from a micro-LED array device 400 according to the present invention where there is no electric crosstalk and open circuit are observed. There is therefore a much improved image contrast.

FIG. 5 is a cross-sectional side view of a micro-LED array 500 according to the present invention. As shown in FIG. 5 there are three mesa regions generally designated 512, 524, 516. The mesa regions 512, 524, 516 protrude upwards and have flat top sections in the form of, for example, truncated cones. The important aspect to note from FIG. 5 is that between mesa regions 512 and 514 there is an open space 518 (i.e. a trench) and no in-filling. Between mesa regions 514 and 516 the space is filled with a non-transparent or substantially non-transparent material 520 to block light. For example, the non-transparent or substantially non-transparent material 520 is a polyimide. In the trench between mesa regions 512 and 514, FIG. 5 shows that light rays 522 exit the lower surface and enter the open space 518 area and are therefore capable of reducing display contrast. In the trench between mesa regions 514 and 516 the non-transparent or substantially non-transparent material 520 blocks the lights rays 524 and prevents the light rays contaminating the area around the LED light emitting areas thereby maintaining a high display contrast.

In the present invention the non-transparent or substantially non-transparent material 520 is therefore introduced (e.g. deposited) to fill the trench between adjacent pixels. Although the actual thickness of the deposited non-transparent or substantially non-transparent material 520 is not important sufficient material should be introduced so that redirected light should be absorbed and prevented from being emitted from the upper surface. The thickness of the non-transparent or substantially non-transparent material 520 may be more or less than the thickness of the mesa structure. Consequently, the light from the LED sidewall can enter the polyimide at a larger range of incident angle owing to the increase in refractive index where the light is then absorbed or partially absorbed by the polymer layer. This helps to further improve display contrast.

The deposited non-transparent or substantially non-transparent material 520 can also function to compensate the height difference of different mesa regions, such that the metal layer on the polyimide can be deposited in a conformal layer, further reducing the light scattering from the trench.

The deposited non-transparent or substantially non-transparent material 520 can also function to effectively isolate each pixel and p-contact from n-contacts, thereby eliminating the undesirable electric crosstalk and improving the device reliability.

Owing to the large refractive index difference between the semiconductor and surrounding mediums a significant portion of the light is typically trapped in the semiconductor layer which leads to phonon recombination effects causing unwanted and potentially damaging thermal build-up. The introduction of a polymer results in more of the light “escaping” plus increases the volume of material and the thermal conductivity to improve heat dissipation. An opaque polymer surface layer can also be formed by annealing the polymer in an oxygen atmosphere.

FIG. 6 is a top view of a micro-LED array 600 according to the present invention where non-transparent or substantially non-transparent material is deposited to fill the trench in adjacent pixels. The emitting LED therefore has a very good display contrast and has a much reduced ‘halo’ effect and crosstalk. The contrast between the LED emitter and the surrounding area is therefore high.

FIGS. 7 to 14 show a method of forming micro-LED arrays according to the present invention. FIG. 7 shows two mesa regions 612, 614 formed by dry etch. In FIG. 8, two pixels 616, 618 are formed on the upper surface of the mesa regions 612, 614. FIG. 9 shows N-bus formation 620, 622 on the upper surface on the mesa regions 612, 614. In FIG. 10 a non-transparent or substantially non-transparent material (e.g. polyimide) 624 is deposited to fill the trench between pixels and as shown extends over the upper surface of the mesa regions 612, 614 and the pixels 616, 618 and the N-bus formations 620, 622. FIG. 11 then shows there is curing of the non-transparent or substantially non-transparent material (e.g. polyimide) 624 with areas 626, 628 etched above the pixels 616, 618. As shown in FIG. 12 metal 630, 632 is spread into and annealed into the etched areas 626, 628. A p-metal 634 is then deposited as shown in FIG. 13. FIG. 14 shows the final array which can be topside and backside emitting.

Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. For example, any suitable type of non-transparent or substantially non-transparent material may be used to block light and improve the display contrast on not only array devices but also flip-chip devices. 

The invention claimed is:
 1. A method of manufacturing a light emitting diode (LED) array comprising: forming a first mesa area of a first LED and a second mesa area of a second LED, wherein a trench is defined between the first and second mesa areas; and filling at least a portion of the trench with a polymeric material having a thickness such that the polymeric material is non-transparent to light emitted from the first and second LEDs and absorbs the light, at least a portion of the light absorbed by the polymeric material from the first LED being reflected from the first mesa area toward the polymeric material.
 2. The method of claim 1, wherein the polymeric material is one of: polymide, epoxy, or benozcyclobutene.
 3. The method of claim 1, further comprising: forming a first pixel on the first mesa area and a second pixel on the second mesa area; filling the polymeric material to extend above the first pixel and the second pixel; etching a first space within the polymeric material above the first pixel of the first mesa area and a second space within the polymeric material above the second pixel of the second mesa area; and depositing a first metal within the first space and a second metal within the second space.
 4. The method of claim 3, further comprising depositing a metal layer on top of the polymeric material to electrically connect the first metal and the second metal.
 5. The method of claim 4, wherein; the first and second mesa areas are of different heights; and the polymeric material provides a conformal layer for depositing the metal layer.
 6. The method of claim 1, wherein forming the first mesa area and the second mesa area includes performing dry etching on a semiconductor layer.
 7. The method of claim 1, further comprising curing the polymeric material subsequent to filling the at least a portion of the trench with the polymeric material.
 8. The method of claim 1, wherein the first and second mesa areas are formed on a semiconductor layer, and the polymeric material at the trench absorbs the light emitted from the first and second LEDs and propagated through the semiconductor layer.
 9. The method of claim 1, wherein filling the at least a portion of the trench with the polymeric material includes annealing the polymeric material in an oxygen atmosphere.
 10. The method of claim 1, wherein the first and second LEDs are micro-LEDs.
 11. The method of claim 1, wherein filling the at least a portion of the trench with the polymeric material includes forming a polymeric material layer over the first and second mesa areas.
 12. A light emitting diode (LED) array, comprising: a first mesa area of a first LED; a second mesa area of a second LED, a trench defined between the first and second mesa areas; and a polymeric material within the trench having a thickness such that the polymeric material is non-transparent to light emitted from the first and second LEDs and absorbs the light, at least a portion of the light absorbed by the polymeric material from the first LED is reflected from the first mesa area toward the polymeric material.
 13. The LED array of claim 12, wherein the polymeric material is one of: polymide, epoxy, or benozcyclobutene.
 14. The LED array of claim 12, wherein: a first pixel is formed on the first mesa area and a second pixel is formed on the second mesa area; the polymeric material within the trench extends above the first pixel and the second pixel; the polymeric material defines a first space within the polymeric material above the first pixel of the first mesa area and a second space within the polymeric material above the second pixel of the second area; and the LED array further includes a first metal deposited within the first space and a second metal deposited within the second space.
 15. The LED array of claim 14, further comprising a metal layer on top of the polymeric material to electrically connect the first metal and the second metal.
 16. The LED array of claim 15, wherein: the first and second mesa areas are of different heights; and the polymeric material provides a conformal layer for the metal layer disposed on top of the polymeric material.
 17. The LED array of claim 12, wherein the first and second mesa areas are formed on a semiconductor layer, and the polymeric material at the trench absorbs the light emitted from the first and second LEDs and propagated through the semiconductor layer.
 18. The LED array of claim 12, wherein the first and second LEDs are micro-LEDs. 